Method of producing an electronic device, electronic device and apparatus for implementing the method

ABSTRACT

The electronic device ( 1 ) of the present invention has a carrier ( 10 ) with a plurality of discrete electro-optical elements ( 110, 130, 150 ) mounted on the surface of the carrier ( 10 ). The electro-optical elements ( 110, 130, 150 ), which cover respective parts of the electrode structure ( 12 ) on the surface of the carrier ( 10 ), each have a polymer layer ( 114, 134, 154 ), which encloses an electro-optical material ( 102, 122, 142 ) between the polymer layer ( 114, 134, 154 ) and the surface of the carrier ( 10 ). The discrete electro-optical elements ( 110, 130, 150 ) have been formed by the individual deposition of discrete droplets of a liquid comprising the electro-optical material and a polymer precursor followed by exposure of the droplets to a stimulus triggering the polymerization of the polymer precursor.

The present invention relates to a method of producing an electronicdevice comprising a plurality of electro-optical elements on a surfaceof a carrier, the carrier surface including an electrode structure.

The present invention also relates to an electronic device comprising acarrier having a carrier surface including an electrode structure and aplurality of electro-optical elements mounted on the carrier surface.

Several electronic devices utilize electro-optical elements to implementa targeted function of the device. Such electro-optical elements can bebased on the principle that the application of an electrical field or acurrent will alter the orientation or configuration of theelectro-optical material, which has an impact on the interaction of thematerial with light. For instance, the electrical field induces a changein orientation or configuration of the electro optical material that mayallow light to pass the electro-optical element, and electro-opticalelements being based on such a principle are therefore also referred toas light-valve elements.

The class of electronic devices including electro-optical elementsinclude electrophoretic displays like e-ink devices and liquid crystaldisplays (LCDs), with the latter having become increasingly popular overrecent years. LCDs can be found in a wide range of products, fromhandheld electronic devices like personal digital assistants and mobilephones to computer monitors and television sets.

Currently, much effort is being put in upscaling the dimensions of theseelectronic devices, e.g. LCDs. However, traditional production methodsof LCDs, in which a liquid crystal material is deposited between twoglass or polymer plates, are not ideal for such efforts, becauseincreasing the size of the substrate panes makes them difficult tohandle. In addition, large substrate panes require large and heavymachinery, which makes the production process costly.

European patent application EP 1065553 A1 discloses an alternativemethod for producing a liquid crystal display. A layer of a mixture of apolymer precursor and a liquid crystal (LC) material is deposited on atransparent substrate carrying an orientation layer, after which themixture is exposed to UV light in a photolithographic step. In thisstep, the polymer precursor is polymerized to form sidewalls between thedesired pixels of the LCD. Subsequently, the rest of the mixture isexposed to UV light. This triggers a phase separation in which thepolymer precursor is polymerized to form a continuous top layer on topof the polymer sidewalls, and in which the LC material is trappedbetween the polymer top layer, the polymer sidewalls and the substrate,thus forming a plurality of pixels on the substrate, with the polymertop layer serving as a second substrate.

However, it is a serious drawback of this method that severalphotolithography steps are still required to form the separate LCpixels, for instance because the development and production of masks iscostly.

Inter alia, it is an object of the present invention to at least reducethe number of required photolithographic steps in the production of anelectronic device according to the opening paragraph.

It is another object to provide an improved electronic device accordingto the opening paragraph.

It is yet another object of the present invention to provide anapparatus for implementing the method of the present invention.

According to an aspect of the present invention, there is provided amethod of producing an electronic device comprising a plurality ofelectro-optical elements on a surface of a carrier, the methodcomprising the steps of depositing a plurality of discrete droplets of afirst liquid on the carrier surface, the first liquid comprising amixture of a first electro-optical material and a first polymerprecursor; and forming the plurality of electro-optical elements byexposing the plurality of discrete droplets to a stimulus forpolymerizing the polymer precursor of a discrete droplet of the firstliquid into a discrete polymer layer enclosing the first electro-opticalmaterial of the discrete droplet between said polymer layer and thecarrier surface. This method will also be referred to as the firstmethod of the present invention.

By depositing discrete droplets of a mixture of an electro-opticalmaterial such as a liquid crystal material and a polymer precursor overthe electrode structure on the carrier surface, the discreteelectro-optical elements, e.g., pixels, are predefined by the droplets.Such an electro-optical element may be formed by a single droplet or, ifdesired, formed by merging a plurality of droplets together bydepositing them on the same location, i.e., on top of each other, on thecarrier surface. This has the advantage that no photolithography step isrequired to acquire separate electro-optical elements. The droplets cansimply be deposited by means of known printing techniques such aspiezo-electric or continuous inkjet printing or bubble jet printing.Depending on the polymer precursor, the polymerization reaction can beinitiated over the whole carrier surface by applying an appropriatestimulus like UV light exposure, heat, electron beam exposure and otherknown suitable polymerization initiators. Consequently, the productionmethod of the present invention is cheaper and more versatile than theprior art production methods.

An additional advantage is that the electronic device size to beproduced on a single carrier can be increased without causing anexcessive increase in production cost, due to the fact thatphotolithographic masks are not necessarily required in the productionprocess of the electronic device of the present invention. Also, thereis no technical limitation to the number of electronic devices that maybe produced on a single carrier, which improves efficiency of theproduction process, thus further reducing production cost.

The carrier surface may be modified by depositing an electrode structuresuch as an interdigitated electrode structure for controlling the liquidcrystal elements with in-plane switching effects. In case of theelectro-optical material being an LC material, the carrier surface maybe modified by depositing an orientation layer such as a rubbedpolyimide alignment layer or a photo-aligning material like a cinnamateor a coumarin containing polymer prior to the deposition of thedroplets, in order to ensure that the LC material adopts the requiredorientation in the electro-optical element. In addition, the carriersurface may be extended with other optical layers such as polarizationfilters, retardation layers, color filters and so on. The LC materialmay be chosen to, for instance, implement electrically controlledbirefringence (ECB), twisted nematic (TN), super twisted nematic (STN),optically compensated birefringence (OCB), vertically aligned nematic(VAN), ferroelectric (FE) or in-plane switching (IPS) LC effects incombination with appropriate electrode structures and alignment layers.

An additional advantage of the production method of the presentinvention is that the shape of the arrangement of the plurality ofelectro-optical elements is no longer governed by the shape of thecarrier surface. By depositing the electro-optical material at the pixellevel, the electro-optical elements can be deposited on a predefinedpart of the carrier surface, thus forming predefined shapes like images.This is particularly advantageous for electronic devices being arrangedto display fixed images.

In an embodiment, the step of depositing the plurality of discretedroplets is preceded by the step of depositing a pattern of wallstructures on the carrier surface for creating a plurality of bordereddomains on the carrier surface, a droplet from the plurality of discretedroplets being deposited in such a bordered domain. The deposition of aplurality of wall structures has the advantage that the wall structuresprevent the individual droplets from further spreading, which preventsdroplets from becoming too thin or from merging with a neighbouringdroplet. Consequently, electro-optical elements having a near flatsurface can be obtained.

Alternatively, the step of depositing a plurality of discrete dropletsis preceded by the step of depositing a plurality of regions of anon-wetting material on the carrier surface. The non-wetting regions maybe used for creating a plurality bordered domains on the carriersurface, a droplet from the plurality of discrete droplets beingdeposited in such a bordered domain. The contact angle of the dropletswith this non-wetting layer is substantially larger than the contactangle of the droplets with the carrier substrate. Consequently, thenon-wetting regions prevent the excessive spreading of droplets andneighbouring droplets from merging.

In a more specific embodiment, before depositing the plurality ofdiscrete droplets, the substrate carrier surface is provided with aplurality of first regions functionalized for selective accumulation ofpolymer material and a plurality of second regions functionalized forselective accumulation of the electro-optical material (102), respectivefirst regions being provided between respective second regions andrespective regions (302) of a non-wetting material. The first and secondregion of selective accumulation facilitate the phase separation intothe polymer layer and the electro-optical material in the desiredmanner. Further, because adhesion between the polymer layer and thecarrier surface is generally improved a mechanically more robuststructure is obtained. The first region may be provided by depositing aseparate layer which partially overlaps or is adjacent (abutting orspaced) with a layer providing the non-wetting regions. The selectivityof the first and second regions is relative in that there is adifferential selectivity in accumulation, for example electro-opticalmaterial may selectively accumulate in the second region because thepolymer material selectively accumulates in the first.

In one embodiment of the method in accordance with the invention thefirst liquid comprises a first colorant which, during formation of theplurality of electro-optical elements, selectively accumulates in thepolymer layer. The colorant may be a dye or a pigment, or a mixture ofdyes and/or pigments and preferably has a color in the visible part ofthe electromagnetic spectrum. Selective accumulation may for example beachieved by choosing a colorant which has a higher solubility in thepolymer layer than in the liquid layer. Selective accumulation isconveniently realized using a colorant which is functionalized withreactive groups adapted to react with the first polymer precursor duringformation of the plurality of electro-optical elements. During formationthe colorant reacts with the polymeric material being formed and becausethe polymeric material phase separates into a discrete polymer layer thefirst colorant is incorporated in the discrete polymer layer. Morespecifically, the first colorant is (co-)polymerizable to form a polymerof the discrete polymer layer. In other words, the first colorant is amonomer of the polymer precursor.

Adding colorant to the mixture reduces the number of steps of theprocess to manufacture a device which requires such a dye, such as a(full) color LCD device. The process of depositing the colorant is alsoself-aligned with the deposition of the liquid.

In another embodiment, the method further comprises the steps ofdepositing a plurality of discrete droplets of a second liquid on thecarrier surface, the second liquid comprising a mixture of a secondelectro-optical material and a second polymer precursor; and forming afurther plurality of electro-optical elements by exposing the pluralityof discrete droplets of the second liquid to a second stimulus forpolymerizing the second polymer precursor into a further discretepolymer layer enclosing the second electro-optical material between saidfurther polymer layer and the carrier surface. These steps arepreferably executed substantially in parallel to improve productionefficiency. Even though the first electro-optical material and thesecond electro-optical material may be the same material, the fact thatthe method of the present invention deposits each electro-opticalelement individually can be used to deposit different types ofelectro-optical material at a single carrier surface. For instance, afirst liquid crystal material and a second liquid crystal material canbe chosen to define different electro-optical elements, e.g., differentcolour pixels. Differently colored discrete elements can be achievedusing a first colorant in the first and a second colorant having a colordifferent from the first. This way, the intended performance of theelectro-optical elements can be improved by depositing the appropriateelectro-optical materials. It will be obvious to those skilled in theart that this approach can be extended to any number of differentliquids, e.g., three different liquids for a RGB colour display device,and so on. For example, an RGB full colour display device may beconveniently realized using in respective first, second and thirdelements, respective red, green and blue colorants which selectivelyaccumulate in the respective polymer layers of the first, second andthird elements. Thus the number of steps required to make such a deviceare reduced and the process of providing the colorants is self-alignedwith the liquid.

After the formation of the electro-optical elements, the electronicdevice may be further processed. For instance, the method of the presentinvention may further comprise the step of depositing a furtherelectrode structure on a polymer layer of the plurality ofelectro-optical elements to produce an electronic device havingelectro-optical elements sandwiched between a bottom electrode structureand a top electrode structure or to produce an electronic device havinga single electrode structure opposite the carrier surface.

In addition, the method may further comprise the steps of covering theplurality of electro-optical elements with a light reflecting coating inthe case of reflective TN, STN, ECB and IPS LC material to provide for alight-reflective electronic device and/or covering the plurality ofelectro-optical elements with a planarization layer to facilitatefurther processing steps on the electronic device. Also, a step ofadding a light-polarizing layer to the carrier may be executed prior toor after depositing the electro-optical elements. This is particularlyuseful in the case of the electronic device being a reflective ortransmissive display having a transparent carrier.

According to a further aspect of the invention, there is provided amethod of producing an electronic device comprising a display area on apart of a surface of a carrier carrying an electrode structure, themethod comprising the steps of dripping a first liquid on the part ofthe carrier surface, the first liquid comprising a mixture of a firstelectro-optical material and a first polymer precursor; and forming thedisplay area by exposing the first liquid to a stimulus for polymerizingthe polymer precursor into a discrete polymer layer enclosing the firstelectro-optical material between said polymer layer and the carriersurface. This method will also be referred to as the second method ofthe present invention.

Rather than depositing droplets with the intention to keep themseparated to obtain discrete electro-optical elements, the printingtechnique of the present invention can also be advantageously applied toproduce electronic devices having a single or a few display areas, e.g.,display devices having a predefined single image, such as a billboard.By dripping the first liquid on a part of the carrier surface, abetter-defined display area can be formed than was the case with priorart deposition techniques such as doctor blading, because spillage ofthe first liquid outside the part of the carrier surface was difficultto avoid with these techniques.

It will be recognized by those skilled in the art that the second methodof the present invention is a special instance of the first method ofthe present invention, because in fact a display device with a singleelectro-optical element rather than a plurality of electro-opticalelements is being formed. Advantageously, the method comprises the stepof bordering the part of the carrier surface with a dewetting materialprior to the dripping of the first liquid on the predefined part. Thiscan yield an even better defined display area.

In an embodiment, the method comprises the step of providing a furthersurface of the carrier with an adhesive layer. Electronic devices thatare formed via the first or second method of the present invention canbe very light-weight, because the use of heavy carriers can be avoided.This for instance allows for such electronic devices to be used assticker displays. This is particularly advantageous for electronicdevices formed by the second method of the present invention, becausesuch devices require very little driver circuitry, e.g., an on/offsignal generator, which can easily be integrated onto or into thecarrier.

Advantageously, the method further comprises the step of integrating apower supply into the carrier. This yields an electronic device that canbe used in many places because the presence of an external power supplyis not required for the operation of the electronic device.

Alternatively, the method further comprises the step of providing thefurther surface with a conductive contact, the conductive contact beingconductively coupled to the electrode structure. This allows for theelectronic device to be formed to be used for a prolongued period oftime, because an external, replenishable power supply can be used.

According to yet another aspect of the invention, there is provided anelectronic device comprising a carrier having a surface and a pluralityof electro-optical elements positioned on the carrier surface, each ofthe electro-optical elements having a discrete first polymer layerenclosing a first electro-optical material between said layer and thecarrier surface.

Such an electronic device can be formed by executing the steps of thefirst method of the present invention. It is emphasized that theaforementioned various advantageous embodiments of said method could beused to produce analogous advantageous embodiments of the electronicdevice of the present invention.

An additional advantage is obtained if the electronic device comprises aflexible carrier. A well-known problem with having a substantiallycontinuous layer of electro-optical elements on a surface of a flexiblecarrier, e.g., a layer of LC pixels as disclosed in EP 1065553 A1, isthat upon bending the surface, the stress on the inner and outersurfaces of the electronic can cause damage to those surfaces, thusdamaging the LC pixels of the electronic device. The electronic deviceof the present invention suffers less, if at all, from this problem,especially when the plurality of discrete electro-optical elements isnot covered by an additional layer. Because the electro-optical elementsare separated from each other, the outer surface does not experiencetensile loading forces when the substrate is bent, thus providing animproved flexible electronic device.

According to a further aspect of the invention, there is provided anapparatus for producing an electronic device comprising a plurality ofelectro-optical elements on a surface of a carrier, the apparatuscomprising receiving means for receiving the carrier and depositingmeans for depositing a plurality of discrete droplets of a liquid on thecarrier surface, the liquid comprising a mixture of an electro-opticalmaterial and a polymer precursor, the depositing means being arrangedopposite the receiving means, with at least one of the receiving meansand the depositing means comprising mechanical translation means forchanging an orientation of the depositing means over a first part of thecarrier surface to an orientation over a second part of the carriersurface. Such an apparatus is capable of depositing the droplets of afirst liquid on the carrier surface in accordance with the method of thepresent invention.

In an embodiment, the apparatus further comprises means for forming theplurality of electro-optical elements by exposing the plurality ofdiscrete droplets to a stimulus for polymerizing the polymer precursorof a discrete droplet of the liquid into a discrete polymer layerenclosing the electro-optical material of the discrete droplet betweensaid polymer layer and the carrier surface. The additional means ensurethat the apparatus is also capable of implementing the step of formingthe polymer layers in accordance with the method of the presentinvention.

Advantageously, the depositing means comprise a printing head having aplurality of nozzles. This increases the efficiency of theimplementation of the method of the present invention, because a largernumber of droplets can be deposited at the same time.

It is a further advantage if a first subset of the plurality of nozzlesis coupled to a reservoir for containing a first liquid comprising amixture of a first electro-optical material and a first polymerprecursor and a second subset of the plurality of nozzles is coupled toa reservoir for containing a second liquid comprising a mixture of asecond electro-optical material and a second polymer precursor. Thisway, droplets having different compositions can be deposited at the sametime, which is particularly advantageous for the production of colourdisplay devices via the method of the present invention.

The invention is described in more detail and by way of non-limitingexamples with reference to the accompanying drawings, wherein:

FIGS. 1-3 schematically depict various embodiments of the first methodand electronic device of the present invention;

FIG. 4 schematically depicts another embodiment of the electronic deviceof the present invention;

FIG. 5 schematically depicts a prior art display device and a displaydevice of the present invention having bent carriers;

FIG. 6 schematically depicts an apparatus for implementing the first orthe second method of the present invention; and

FIG. 7 depicts an electronic device formed by the second method of thepresent invention.

It should be understood that the Figures are merely schematic and arenot drawn to scale. It should also be understood that the same referencenumerals are used throughout the Figures to indicate the same or similarparts.

FIG. 1 a shows a carrier 10 including an optional electrode structure12. It is emphasized that FIG. 1 and the following Figs. show anembedded electrode structure 12 for reasons of clarity only. It shouldbe understood that the surface of the carrier 10 preferably may also bedefined by placement of the electrode structure 12 on top of the carrier10. The electrode structure 12 can be formed on top of the carrier 10from known materials, e.g., Indium Tin Oxide (ITO), and by knowntechniques for forming electrode structures on a carrier 10. The carrier10 may comprise any suitable material, e.g., glass, polymer, or evennon-obvious materials as modified wood, ceramics or modified paper.Optionally, the surface of carrier 10 that carries the optionalelectrode structure 12 may also be further modified prior to theformation of the electro-optical elements on the surface. For instance,if the electro-optical elements are light valves utilizing lightpolarization effects, e.g., liquid crystal elements, a light-polarizinglayer 14 may be deposited on the surface of carrier 10 prior to theformation of the electro-optical elements on the carrier surface. Thelight-polarizing layer 14 may be formed from known light-polarizingmaterials. Alternatively, a light-polarizing layer may be placed on afurther surface of the carrier 10 substantially in parallel with thesurface including the electrode structure 12. In addition, an optionalorientation layer 16 may be deposited on the surface of carrier 10. Theorientation layer 16 may be formed from known materials such aspolyimides, which may be a rubbed polyimide such as Al3046, which issupplied by the JSR electronics company of Japan to achieve a desiredorientation direction of an electro-optical material like a liquidcrystal material. Alternatively, photo-aligning materials such ascinnamates and coumarin may be used, which induce orientation in anelectro-optical material like a liquid crystal material after beingexposed to linearly polarized light.

In a next step, the precursors for a plurality of electro-opticalelements are deposited on the surface of carrier 10. The result of thisdepositing step is shown in FIG. 1 b, where a plurality of discretedroplets 100, 120 and 140 have been deposited on the carrier surface.The deposition can be achieved by means of known printing techniquessuch as piezo-electric inkjet printing, continuous printing and bubblejet printing. The droplets may have been deposited as single droplets oras a deposition of a plurality of droplets in one location in order toachieve a large droplet comprising a plurality of smaller droplets. Theprinter used for the deposition of the droplets 100, 120 and 140 may bea multi-nozzle printer, in which case the droplets 100, 120 and 140 maybe printed at the same time in a parallel printing step, which makes theproduction process of the electronic device more efficient.

The droplets 100, 120 and 140 may all be of a first liquid, the firstliquid comprising a mixture of a first electro-optical material 102,122, 142 and a first polymer precursor 104, 124, 144, in which case theplurality of electro-optical elements to be formed from droplets 100,120, 140 are all of the same type. A polymerization initiator may alsobe present in the liquid to start a polymerization reaction uponsubjecting the droplets to an appropriate stimulus. As emphasizedbefore, the droplets 100, 120 and 140 can be printed onto the carrier 10using known printing techniques.

The individual deposition of the droplets has the large advantage thatthe liquids from which droplets 100, 120 and 140 are formed can bechosen to differ from each other in that at least the electro-opticalmaterials 102, 122 and 142 are different in each liquid. Optionally, thepolymer precursors 104, 124, 144 as well as the polymerizationinitiators may also be different. When the electro-optical materials102, 122 and 142 are different in each liquid, several pluralities ofdifferent electro-optical elements may be formed, which for instance maybe beneficial if the electro-optical elements are to define RGB pixelsof a colour display device, in which case different electro-opticalmaterials 102, 122 and 142 can be chosen to generate RGB pixelsincluding an electro-optical material that is particularly suited forthat pixel type. Alternatively, an RGB full colour display device may beconveniently realized using in respective first, second and thirdelements, respective red, green and blue colorants which selectivelyaccumulate in the respective polymer layers of the first, second andthird elements. Thus the number of steps required to make such a deviceare reduced and the process of providing the colorants is self-alignedwith the liquid.

The printing of several pluralities of droplets can for instance beachieved by using the various nozzles of a multi-nozzle printer to printdroplets having such differing compositions, e.g., a first nozzle beingarranged to print a first liquid comprising a mixture of a firstelectro-optical material and a first polymer precursor and a secondnozzle being arranged to print a second liquid comprising a mixture of asecond electro-optical material and a second polymer precursor. Anotheroption to further optimize the production process is to use a differentmulti-nozzle head for the deposition of each of the various liquids.

In a next step, the droplets 100, 120 and 140 are exposed to a stimulusfor initiating a polymerization reaction of the polymer precursor 104,124 and 144 to transform the droplets 100, 120 and 140 intoelectro-optical elements 110, 130 and 150. Such a stimulus may forinstance be exposure to UV light or heat if the polymerization reactionto be induced in the respective droplets 100, 120 and 140 is of aphoto-induced or thermally induced type, respectively. Obviously, asuitable polymerization initiator has to be chosen accordingly.Polymerization can also be directly induced by an electron beam.

Upon exposure of the droplets to the stimulus, the photo-initiatedpolymerization reaction takes place at the surface of the droplets 100,120 and 140 and triggers a phase-separation within these droplets.Consequently, the respective electro-optical materials 102, 122 and 142are enclosed between the surface of the carrier 10 and the respectivelyformed discrete polymer layers 114, 134 and 154.

A non-limiting example of a suitable composition of a first liquid to bedeposited in droplet form as electro-optical element precursors on acarrier is as follows:

50 weight percent (wt %) of a liquid crystal mixture, for instance themixture E7, which is marketed by Merck, the liquid crystal mixture beingan embodiment of the electro-optical material 112;

44.5 wt % photo-polymerizable isobornylmethacrylate (supplied bySartomer) and 4.5 wt % of a stilbene dimethacrylate dye

, the synthesis of which has been disclosed in PCT patent application WO02/42382 and which is hereby incorporated by reference, the twoacrylates being an embodiment of the polymer precursor 114; and

0.5 wt % benzildimethylketal, which is marketed by Ciba-Geigy under thetrade name Irgacure 651.

Optionally, a colorant which selective accumulates in the polymer layerupon photo-polymerization may be included. The colorant may for examplebe an azo dye functionalized with a reactive group such as a(meth)acrylate group such as the dye

This dye has an absorption peak around 400 nm.

A non-limiting example of the printing process of the present inventionusing the embodiment of the first liquid given above is as follows. In atest setup, a 6×6 inch square glass carrier 10 was provided with aninterdigitated electrode structure 12 and a rubbed polyimide orientationlayer Al3046 from the JSR electronics Company of Japan. The dimensionswere chosen to fit 9 small displays on the carrier 10. It is emphasizedthat much larger dimensions for the carrier 10 are equally feasible,however. The carrier 10 was mounted on a computer controlled X-Y tablehaving a variable speed of 1-30 mm/s.

A MicroDrop inkjet printing device was placed in a fixed position overthe X-Y table. The dispensing head of the MicroDrop inkjet printingdevice included a glass capillary shaped into a nozzle on one side, thecapillary being surrounded by a tubular piezo-activator for generating apressure wave through the capillary. The pressure wave triggers therelease of a droplet of the first liquid from the capillary. The shapeof the pressure wave as well as the diameter of the capillary nozzle canbe varied to control the size of the droplets to be released. Here, apressure wave having a single block shape and a 70 micron nozzle havebeen used, leading to droplet diameters of 60-75 micron at the nozzleexit, each droplet having having a volume of around 70 picoliter. Eachof the droplets 100, 120 and 140 were formed on the carrier 10 bydepositing 75 droplets over a single part of the electrode structure 12.

The droplets 100, 120 and 140 were exposed to UV light from a PhilipsTL08 UV lamp with a light intensity of 0.1 mW/cm² for 30 minutes at 40°C., after which the formation of the electro-optical elements 110, 130and 150 was completed.

The inclusion of a compound having a chromophore strongly absorbing inthe UV region of the electromagnetic spectrum, i.e., the stilbenedimethacrylate dye in the example above, causes a gradient in the UVintensity through the droplets 100, 120 and 140. This effect may beamplified by the UV absorptions of the other components of the liquidsused to form these droplets, like the other components of the polymerprecursors 104, 124 and 144 and the electro-optical materials 102, 122and 142. Consequently, the polymerization reaction predominantly takesplace at the surface of the droplets 100, 120 and 140 facing the UVsource. When other stimuli for triggering the polymerization reactionare used, care has to be taken that the polymerization reactionpredominantly takes place at the surface of the droplets 100, 120 and140.

At this point, it is emphasized that the viscosity of the liquid has amarked influence on the printing process. For instance, the operationalink viscosity range of suitable piezoelectric inkjet printers rangesfrom approximately 1-20 mPa·s. It should be understood that other rangesmay be appropriate for different types of printing devices. If theliquid has a higher viscosity, heating of the nozzles of the printer ispreferred to lower the viscosity. Apart from heating, the viscosity ofthe liquids used in the printing process from which the droplets 100,120 and 140 are formed may also be controlled in a number of alternativeways.

A first option is to add an inert solvent to the liquid to lower itsviscosity, like anisole or xylene. However, care has to be taken thatthe solvent is not too volatile, because this may lead to the solventevaporating from the liquid before it has left the nozzle of theprinter. This can lead to blockage of the printer nozzle, since thisnozzle may be no more than a few tens of microns wide. Also, theevaporation speed of the solvent should not be too low, since this willslow down the process of the solvent evaporating from the droplets 100,120 and 140, which has a negative impact on the production speed of theelectronic devices of the present invention. It has been found thatsolvents having a vapour pressure in the range from 0.04 kPa to 4 kPa at298 K are most suitable for such an application. Care also has to betaken that the fraction of solvent remaining in the droplets 100, 120and 140 is low enough before initiating the polymerization of thepolymer precursors, because the solvent otherwise may interfere with thephase separation or with the correct functioning of the electro-opticalmaterial.

Alternatively, the various components that make up the liquids can bechosen to modify the viscosity of the liquid. For instance, the liquidcrystal mixture E7 may be replaced by a lower viscosity liquid crystalmaterial like the single component cyanobiphenyl liquid crystal marketedby Merck under the name K15 to lower the viscosity of the liquid givenin the aforementioned example.

Also, a low viscous and volatile reactive monomer may be used to tunethe viscosity of the liquids used as printing inks. Prior to thepolymerization of the polymer precursors 104, 124 and 144, most of thevolatile reactive monomer will already have evaporated and the remainingfraction will be incorporated in the polymer layers 114, 134 and 154,thus causing no interference with the electro-optical properties of theelectro-optical materials 102, 122 and 142.

It is pointed out that in the case of multi-component electro-opticalmaterials, the polymerization process may alter the composition of theelectro-optical materials 102, 122 and 142, because some of the variouscomponents of the electro-optical materials may be partially enclosed inthe respective polymer layers 114, 134 and 154. This can be an unwantedphenomenon if the electro-optical properties of the electro-opticalelements 110, 130 and 150 are affected as a consequence.

This can be avoided by formation of a small number of electro-opticalelements on a small test carrier, with subsequent evaluation of thecomposition of the electro-optical materials in those electro-opticalelements by for instance high performance liquid chromatography (HPLC).If the concentration of a component of the electro-optical material isdiscovered to be lower than intended, the fraction of this component inthe first liquid can be increased and the test formation of theelectro-optical elements can be repeated until the electro-opticalmaterials in the electro-optical elements have the desired composition.

FIG. 1 c schematically depicts the formed electro-optical elements 110,130 and 150, which have been formed from respective droplets 100, 120and 140. The electro-optical elements 110, 130 and 150, which mayoperate as pixels of a display device, have respective polymer layers114, 134 and 154, which respectively have been formed from polymerprecursors 104, 124 and 144, and which respectively enclose theelectro-optical materials 102, 122 and 142 between their inner surfacesand the surface of carrier 10. This way, a plurality of electro-opticalelements is formed that each have a discrete polymer layer with asubstantially uniform thickness from the first contact point with thesurface of the carrier 10 to the second contact point with the surfaceof the carrier 10. The electronic device 1 shown in FIG. 1 c may be theend product, in which case the electrode structure 12 may be anelectrode structure suitable for controlling the electro-opticalmaterials 102, 122 and 142 from a single side using in-plane switching.This can for instance be achieved using an interdigitated electrodestructure.

At this stage, it is pointed out that the use of the wording ‘discrete’to define a property of the droplets 100, 120 and 140 or a property ofthe polymer layers 114, 134 and 154, should not be interpreted to meanthat the droplets 100, 120 and 140 or the polymer layers 114, 134 and154 have to be completely separated from each other. Minor contact areasbetween the droplets 100, 120 and 140 or the polymer layers 114, 134 and154 may exist near the surface of the carrier 10 without departing fromthe scope of the present invention. It will be understood that the sizeof such contact areas between two neighbouring droplets will have toremain small enough to prevent neighbouring droplets from merging.

In FIG. 1 d, an optional further processing step on the electronicdevice shown in FIG. 1 c is depicted. In this step, a planarizationlayer 24 is deposited on top of the plurality of electro-opticalelements 110, 130 and 150. The planarization layer 24, which may beformed from any known suitable planarization material, facilitates thedeposition of further layers such as a polarizing layer (not shown) orthe deposition of a further electrode structure 32 on the plurality ofelectro-optical elements 110, 130 and 150 opposite to the electrodestructure 12, as shown in FIG. 1 e. If, however, the electro-opticalelements 110, 130 and 150 are flat enough, the planarization layer 24may be omitted and the further electrode structure 32 may also bedeposited directly on top of the polymer walls 114, 134 and 154 of therespective electro-optical elements 110, 130 and 150.

The further electrode structure 32 and the electrode structure 12 mayform the rows and columns of the electronic device 1. Alternatively, thefurther electrode structure 32 may be an interdigitated electrodestructure to facilitate in-plane switching of the electro-opticalelements, in which case electrode structure 12 may be omitted. Thefurther electrode structure 32 may be formed from the polymersemiconductor material polyethylenethioxythiophene (PEDOT) or similarmaterials that have the advantage that they can be processed at atemperature low enough to avoid damage to the electro-optical elements110, 130 and 150.

Alternatively, the layer 24 may be formed of a light reflecting coatingin the case of the electro-optical materials 112, 132 and 152 comprisingreflective TN, STN, ECB and IPS LC materials, to form a reflectivedisplay device. It should be obvious to those skilled in the art that,where possible, the aforementioned processing steps may be combined orinterchanged without departing from the teachings of the presentinvention.

At this point, it is emphasized that the droplets 100, 120 and 140 inFIG. 1 b and the electro-optical elements 110, 130 and 150 in FIG. 1 chave been represented having a hemispherical shape by way ofnon-limiting example only. A hemi-spherical shape may be preferable inapplication domains where the electro-optical elements need to havelens-like characteristics, in which case the width W of the formedelectro-optical element is of a similar magnitude as height H. Incontrast, in application domains where the electro-optical elements haveto operate as light valves, e.g., LCDs and electrophoretic displays likeE-ink displays, it may be preferable to have droplets with flattenedsurfaces in order to avoid unwanted optical effects, in which case widthW can be much larger than height H. For example, W may be 1,000 micronor more, whereas H may typically be a few tenths of microns.

The shape adopted by the electro-optical elements 110, 130 and 150 canbe controlled by modifying the contact angle α of the droplets 100, 120and 140 with the surface of the carrier 10. A low contact angle α, i.e.a good wetting, facilitates the formation of a thin electro-opticalelement having a relatively flat surface, especially if the element isformed from a large droplet formed by depositing a plurality of smallerdroplets in the same location at the surface of the carrier 10. In caseof an LCD, electro-optical elements 110, 130 and 150, having arelatively flat surface can be especially advantageous when theelectronic device 1 is a display device, because the light passingthrough such electro-optical elements at most experiences minordistortion, thus yielding a display device having a good image quality.When the contact angle α of the discrete droplets 100, 120 and 140 withthe carrier 10 is low, care has to be taken that the discrete droplets100, 120 and 140 do not merge with neighbouring discrete droplets. Also,height H of the droplets should be large enough to enable the properfunctioning of the electro-optical materials 102, 122 and 142 in thecorresponding electro-optical elements 110, 130 and 150. This isparticularly relevant if the electro-optical materials 102, 122 and 142are LC materials, in which case the height H of the electro-opticalelements 110, 130 and 150 should be substantially constant throughoutthe full width W of the electro-optical elements 110, 130 and 150 toensure a proper LC effect in the electro-optical elements 110, 130 and150. Furthermore, prevention of excessive spreading of the droplets 100,120 and 140 will improve the resolution of the electronic device to beproduced.

To enable the droplets 100, 120 and 140 to be printed on the surface ofthe carrier 10 assuming the desired form, the surface of carrier 10 maybe modified prior to the deposition of the droplets 100, 120 and 140. InFIG. 2, an example of such a modification is shown. FIG. 2 a shows thecarrier 10 with an electrode structure 12, an optional polarizationlayer 14 and an optional orientation layer 16 on its surface, on which aphotosensitive lacquer 200 is deposited. The photosensitive lacquer 200is patterned in a photolithography step to form a pattern of wallstructures 202 on the surface of the carrier 10, as shown in FIG. 2 b.The pattern of wall structures 202 forms a relief pattern on the surfaceof the carrier 10. Alternatively, such a relief pattern can for instancealso be obtained through photo-embossing, injection moulding,screenprinting, microcontact printing or two-step photo-polymerizationtechniques.

Next, the droplets 100, 120 and 140 are deposited in separate cavitiesbetween the wall structures 202 formed on the modified carrier 10,leading to an intermediate electronic device as shown in FIG. 2 c. Thedeposition of the droplets 100, 120 and 140 into a bordered area has theadvantage that spreading of the droplets is prevented and that the areacan be filled up, thus providing droplets 100, 120 and 140 having asufficient height H. At this point, it is emphasized that the shape ofthe wall structures 202 is not limited to the shape shown in thisexample. For instance, tapered walls or a multitude of stacked polymerlayers forming the walls may also be used without departing from thescope of the present invention.

Furthermore, it will be understood that the modification steps of thesurface of the carrier 10, e.g., the deposition of the optionalorientation layer 16, may also take place after the development of thewall structures 202.

An alternative carrier modification method to achieve these advantagesis shown in FIG. 3. In FIG. 3 a, a stamp 300 such as apolydimethylsiloxane (PDMS) stamp is used to print regions 302 of anonwetting material on the surface of the carrier 10. If required, theregions 302 may be offset printed on top of an optional orientationlayer 16, such as the aforementioned Al3046. As an ink for the PDMSstamp 300, a homeotropic alignment material such as SE7511 from theNissan Chemical Company from Japan may be used, although the use ofother known offset printing inks, e.g., polyimides, is also possible.

The printing of the regions 302, which may be done with a stampsimultaneously contacting the whole surface of the carrier 10 or with astamp that is rolled over the surface of the carrier 10, provides aplurality of bordered domains on the carrier surface, as shown in FIG. 3b. The nonwetting regions 302 ensure that the wetting on the surfacecarrier 10 predominantly takes place in the bordered domains upondeposition of the droplets 100, 120 and 140, thus yielding anintermediate structure of the electronic device as shown in FIG. 3 c.Good nonwetting properties of the carrier surface can be achieved bychoosing a nonwetting material, e.g., the aforementioned SE7511, whichcauses the contact angle E of the droplets 100, 120 and 140 with thecarrier 10 to be at least 10 degrees larger at the regions 302 comparedto the contact angle □ with the untreated regions of the carrier 10.

Rather than using offset printing, the regions 302 of a dewettingmaterial may be also be deposited by alternative printing techniquessuch as microcontact printing, flexo-graphic printing, screen printing,inkjet printing, gravure printing, gravure-offset printing or tamponprinting.

Optionally, before depositing the plurality of discrete droplets, thesubstrate carrier surface is provided with a plurality of first regionsfunctionalized for selective accumulation of polymer material and aplurality of second regions functionalized for selective accumulation ofthe electro-optical material (102), respective first regions beingprovided between respective second regions and respective regions (302)of a non-wetting material. Having such regions facilitates phaseseparation in the desired manner and improves mechanical stability ofthe structure obtained after phase separation because the first regiongenerally improve adhesion between the carrier surface and the polymerlayer. The first and second regions may be regions of high and lowaffinity, respectively, for precursor polymer. Mechanical stability isparticularly improved if the high affinity regions are functionalizedwith chemically reactive groups and the regions of low affinity are notso functionalized, the chemically reactive groups being adapted to reactwith the polymer precursor. Alternatively or in addition, the first andsecond regions can be functionalized for facilitating a high and lowrate of polymerization respectively. This can be achieved by means of alow (including zero) and high concentration of polymerization inhibitorin the first and second region respectively.

Material for forming the first and/or second regions are known in theart per se. Example of materials for forming first regions provided withreactive groups and physical bonding of the first region to theunderlying carrier surface include polymers or oligomers with reactiveside-chains such as (meth)-acrylate side chains, optionally diluted withinert solvent for ink jet printability. An example of such a polymer isa photosensitive polyimide precursor, more particular a polyamic estercontaining acrylate side chains dissolved in N-methylpyrrolidone such asDurimide™ available from Arch chemicals, a typical molecular structureof which is shown below.

Also suitable, in case of acrylate reactive groups, are polymers oroligomers containing amine groups. Amine groups react with acrylategroups in a Michael's addition reaction. The amine groups can beincorporated into the carrier in a patterned way. But also possible isto print on top of the carrier a pattern of polyimide precursor polymer.This precursor is not or only partly cured after printing such thatreactive units remain available.

Multifunctional (meth-)acrylate monomers or a mixture thereof and aphoto initiator may also be used. Bisphenol A di(meth)acrylate ortripropyleneglycoldiacrylate are good candidates. After printing, themixture can be partly polymerized by a UV exposure. This ensures theimmobilization of the printed patterns. The groups that have not reactedcan be used for chemical bonding to the polymer formed during thestratification process. The mixture needs a sufficient high viscosity,to prevent it from spreading over the carrier surface after printing.

First regions can also be chemically bonded to the carrier surface aswell as the polymer layer. This can be achieved for example by means offunctionalized (chloro)silanes in combination with a polyvinylalcohol(PVA) carrier surface. Chloro-silanes chemically bond with the hydroxylgroups of the PVA. Since the silanes are micro contact printable, apatterned monolayer of for example (meth)-acrylatechlorosilanes can beprinted. The polymer precursor is selected to be capable of reactingwith the (meth)acrylate groups of the silane.

Carrier surfaces of cinnamate or coumarine type of photo-alignmentmaterials in combination with thiols can also be used to form firstregions having reactive groups.

Obviously, the type of reactive group to use depends on the polymerprecursor. For example if the precursor polymer is a thiolene, thematerial for the first region may be an (meth)acrylate, a vinyl, a thiolgroups or an amine compound. Epoxide precursor polymers cured bycationic polymerization can be combined with printed structurescontaining epoxide, amine, acid, acide anhydride, acid chloride groups.

Further materials which can be suitably used to provide the first andsecond regions are available in the art as such. For details, referenceis made to the European patent application with application number03102443.3 filed by Applicant and European patent application withapplication number 03102445.8 filed by Applicant and the applicationswhich claim the priority of each thereof, the content of all of which isincorporated by reference.

The non-wetting and/or first region and/or second region may be providedin any desired pattern to provide the electro-optical elements with adesired outline. A grid or pattern of squares may be used, which forexample corresponds to pixel boundaries of a display. Other shapes canbe also applied such as a hexagonal shape to make a honeycomb structure,which is known to have outstanding mechanical properties. Circularlyshaped structures can also be made. The sizes of the structures can bechosen the same or different from the pixel size. For instance largerwhere several pixels are enclosed or, oppositely smaller where eachpixel contains more than one encapsulated liquid crystal capsule. Thethickness of the non-wetting, first and/or second regions can be chosendifferently. The thickness can be of the order of 1 nanometer (in thecase of a monomolecular silane layer) to several hundreds of nanometersin case of printed polyimide. In such cases, the polymer layer wouldtypically provide the wall of the electro-optical elements. But ofcourse thicker layers can be printed that form a substantial part of thepolymer walls or are substantially form the walls of the electro-opticalelements.

The first and/or second regions may be provided before or afterdepositing the non-wetting regions (302). The first regions maypartially overlap with the region 302 or provided adjacent thereto(abutting or spaced). Methods suitable for depositing the non-wettingregions may also be used to provide the first and second regions.

A convenient way to apply a non-wetting region on top of a first regionformed of the reactive polyimide described above is offset printing amonolayer of an amphiphilic material having at one side a group that iscapable reacting with the acrylate group of the reactive polyimidematerial and at the other side an apolar tail like alkyl groups orfluorinated alkyl groups. Example of such an amphiphilic compound is analkylthiol (e.g. octadecyl thiol). The thiol reacts with the acrylatedouble bond of the reactive polyimide under the action of heat or UVlight in the presence of a free radical initiator, such as an alkylamine(e.g. octylamine).

As opposed to having separate nono-wetting and first regions, thenon-wetting region may be provided with reactive groups capable ofreacting with the precursor polymer thus saving one patterned depositionstep. A homeotropic polyimide alignement material functionalized with(meth)acrylate groups may be used for this purpose.

In FIG. 4, an advantageous embodiment of an electronic device 1according to the present invention is depicted. A predefined part of thesurface of carrier 10 of the electronic device 1 carries a plurality ofelectro-optical elements 110 arranged in a corresponding predefinedpattern. It will be appreciated by those skilled in the art that withthe production method of the present invention, such an electronicdevice 1 can be easily produced, because the whole surface of thecarrier 10 can be equipped with a regular electrode structure (notshown), with the predefined pattern of the electronic device beingbuilt-up by means of a plurality of discrete electro-optical elements110, or, several pluralities of electro-optical elements, e.g.,electro-optical elements 110, 130 and 150 as previously shown. Ratherthan having to shape an electrode structure in a predefined pattern andcover the whole surface of the carrier 10 with electro-optical elements,which is a time-consuming and costly process typically associated withsegmented display devices, the method of the present invention allowsfor a more facile way of producing such an electronic device, becausethe electro-optical elements 110 can be produced individually on top ofthe regular electrode structure, thus yielding a more simple and cheaperelectronic device 1 that can be produced faster.

The fact that the electro-optical elements 110 are individually formedon the surface of carrier 10 also facilitates the formation ofelectronic devices 1 and in particular display devices having anon-rectangular shape, because the formation of the electro-opticalelements 110 is no longer related to the shape of carrier 10. In fact,the shape of the carrier 10 may be any shape that allows the formationof a functioning electrode structure on its surface.

The electronic device 1 of the present invention also has particularadvantages when the carrier 10 is a flexible carrier. FIG. 5 aschematically depicts an electronic device 500 in a bent state. Theelectronic device 500, which can be produced using prior art productionmethods, such as for instance disclosed in PCT patent application WO99/21052, has a plurality of electro-optical elements 520, which aretypically separated by polymer walls or lithographic spacers 525 andwhich are sandwiched between a flexible carrier 510, which may be formedfrom a thin polymer such as a modified polycarbonate foil marketed bythe Tejin company, and a polymer layer 530, which is sealed to theflexible carrier 510. Due to the presence of the top layer 530, thecarrier 510 experiences an inward directed stress force in the bentstate as indicated by arrows 540, whereas the top layer 530 experiencesan outward directed stress force indicated by arrows 550. This causes astress load on the electronic device 500 that may lead to the failure ofthe device. Also, the electro-optical elements 510 can deform under suchstress loads, which in particular in the case of the electro-opticalmaterial in these elements being an LC material causes deterioration ofthe display qualities such as variations in the grey scales of thevarious electro-optical elements 510 of the electronic device 500.

In comparison, FIG. 5 b shows an electronic device 1 according to thepresent invention. The electronic device 1 has a flexible carrier 10,which may be formed from the same polymer substrate as that ofelectronic device 500 or another suitable flexible material, the carrier10 carrying a plurality of discrete electro-optical elements 110 on itssurface. Because the electro-optical elements 110 of the electronicdevice 1 of the present invention are not formed by a continuous layersuch as a polymer layer 530 but are formed by separate discrete polymerlayers 114 instead, the electronic device 1 is not subjected to a stressload upon bending of the carrier 10. Consequently, the performance ofthe electronic device 1 in general and of the electro-optical elements110 in particular is not compromised when the electronic device is bent.

A further advantage of applying the present invention to flexiblesubstrates is that the electro-optical elements of the present inventiontypically only have a height H as shown in FIG. 1 c of a few tenths ofmicrons, thus having a positive effect on the reduction of the overallthickness of the flexible electronic device. This is of particularrelevance to matrix array electronic devices based on organicsemiconductor materials, because the electro-optical printing techniqueof the present invention can be performed at temperatures that are lowenough to ensure that the organic semiconductor materials are keptintact. In addition, such an electronic device 1 can be kept thin enoughto be rolled up, without causing excessive stress to the various layersof the electronic device in its rolled-up state.

FIG. 6 shows an embodiment of an apparatus 600 for producing anelectronic device 1 comprising a plurality of electro-optical elementson a surface of a carrier 10 by implementing the method of the presentinvention. An XY-table 620 is arranged to receive the carrier 10, whichin this case carries an electrode structure 12. In the example shown inFIG. 6, 9 electrode structures 12 corresponding with 9 electronicdevices to be produced are depicted as a non-limiting example only. TheXY table 620 can be translated over tracks 624 under control of computersystem 622.

Opposite the surface of the XY table 620 that carries the substrate 10,the apparatus 600 preferably includes a plurality of printing devices640 in a fixed construction 644, although a single printing device 640is also feasible. The printing devices 640 are arranged to deposit aplurality of discrete droplets of a liquid on the carrier surface. Tothis end, each of the printing devices 640 preferably includes aprinting head 641 having a plurality of nozzles 642 with their outletspointed towards the XY table 620, although single-nozzle printing heads641 are also feasible. All of the nozzles 642 may be attached to asingle reservoir (not shown) for containing a first liquid comprising amixture of a first electro-optical material 102 and a first polymerprecursor 104, in which case all the electro-optical elements to beformed will contain the same electro-optical material.

Alternatively, a subset of the nozzles 142 may be attached to areservoir (not shown) for containing a first liquid comprising a mixtureof a first electro-optical material 102 and a first polymer precursor104, while another subset of the nozzles 142 may be attached to areservoir for containing a second liquid comprising a mixture of asecond electro-optical material 122 and a second polymer precursor 124,in which case different types of electro-optical elements can bedeposited in parallel. Also, the printing devices 640 may comprise aplurality of printing heads 641 to further optimize the printing processof the present invention. The printing devices 640 may be known printingdevices such as piezo-electric or continuous inkjet printing devices orbubble jet printing devices.

Preferably, the apparatus 600 also comprises means for forming theplurality of electro-optical elements such as an UV-lamp (not shown) ora heat source (not shown).

It will be understood by the skilled person that instead of having atranslation table 620, fixed means 620, e.g., a fixed table, forreceiving the carrier 10 and a plurality of printing devices 640 in a XYtranslation construction 644 can also be used without departing from thescope of the present invention. Furthermore, it will be obvious that theapparatus 600 can also be used to deposit the first liquid in accordancewith the second method of the present invention by allowing the mergingof the deposited droplets.

FIG. 7 depicts an electronic device 700 obtained with the second methodof the present invention. The electronic device 700 has a carrier 10with an electrode structure 12, e.g., an interdigitated electrodestructure, on its surface. Parts 722 and 724 of the surface of thecarrier 10 are covered with an electro-optical material encapsulatedbetween a polymer layer (not shown) and the carrier surface. The parts722 and 724, which form the display area of the electronic device 700,has been formed by dripping a plurality of droplets of a first liquidcomprising a first electro-optical material 102 and a first polymerprecursor 104 on the respective parts, after which the display area hasbeen formed by exposing the first liquid to an appropriate stimulus inanalogy with the first method of the present invention. To furtherimprove the definition of the parts 722 and 724, a border of a dewettingmaterial (not shown) may have been deposited around the parts 722 and724. It is emphasized that an unlimited range of different shapes can bedefined for the display area with the second method of the presentinvention, including areas which almost completely cover the surface ofthe carrier 10.

The electrode structure 12 is conductively coupled to control circuitry740, which may be as simple as an on/off signal generator. The controlcircuitry 740 may be responsive to an on/off switch (not shown). Thepower to be supplied to the electrode structure 12 may be provide by anintegrated power supply (not shown) such as a battery, or by an externalpower source via a conductive contact (not shown) at a further surfaceof the carrier 10. The further surface may be extended with an adhesivelayer 750 to allow the electronic device 700 to be used as a displaysticker or as a display laminate. Such a display laminate may becombined with modular toys, e.g., LEGO, with a toy module comprising amatching conductive contact to connect a conductive contact of theelectronic device 700 to a power supply. This for instance enables theuse of a toy module as a separate ‘pixel’ in a modular display device,for instance by adhering electronic devices 700 with different colourappearances to different toy modules.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.The word “comprising” does not exclude the presence of elements or stepsother than those listed in a claim. The word “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention can be implemented by means of hardware comprising severaldistinct elements. In the device claim enumerating several means,several of these means can be embodied by one and the same item ofhardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

1. A method of producing an electronic device comprising a plurality ofelectro-optical elements on a surface of a carrier the method comprisingthe steps of: depositing a plurality of discrete droplets of a firstliquid on the carrier surface, the first liquid comprising a mixture ofa first electro-optical material (102) and a first polymer precursor andforming the plurality of electro-optical elements by exposing theplurality of discrete droplets to a stimulus for polymerizing thepolymer precursor of a discrete droplet of the first liquid into adiscrete polymer layer enclosing the first electro-optical material ofthe discrete droplet between said polymer layer and the carrier surface.2. A method as claimed in claim 1, wherein a discrete droplet of thefirst liquid is formed by depositing a plurality of smaller droplets ofthe first liquid over a same respective part of the electrode structure.3. A method as claimed in claim 1, wherein the step of depositing aplurality of discrete droplets is preceded by modifying the carriersurface by depositing an electrode structure on the carrier surface. 4.A method as claimed in claim 1, wherein the step of depositing aplurality of discrete droplets is preceded by modifying the carriersurface by depositing an orientation layer on the carrier surface.
 5. Amethod as claimed in claim 1, wherein the step of depositing theplurality of discrete droplets is preceded by the step of depositing apattern of wall structures on the carrier surface for creating aplurality of bordered domains on the carrier surface, a droplet from theplurality of discrete droplets being deposited in such a bordereddomain.
 6. A method as claimed in claim 1, wherein the step ofdepositing a plurality of discrete droplets is preceded by the step ofdepositing a plurality of regions of a nonwetting material on thecarrier surface.
 7. A method as claimed in claim 6, wherein, beforedepositing the plurality of discrete droplets, the substrate carriersurface is provided with a plurality of first regions functionalized forselective accumulation of polymer material and a plurality of secondregions functionalized for selective accumulation of the electro-opticalmaterial respective first regions being provided between respectivesecond regions and respective regions of a non-wetting material.
 8. Amethod as claimed in claim 1, wherein the first electro-optical materialcomprises a liquid crystal material.
 9. A method as claimed in claim 1,wherein the first liquid comprises a first colorant which, duringformation of the plurality of electro-optical elements, selectivelyaccumulates in the polymer layer.
 10. A method as claimed in claim 9,wherein the first colorant is functionalized with reactive groupsadapted to react with the first polymer precursor during formation ofthe plurality of electro-optical elements.
 11. A method as claimed inclaim 10, wherein the first colorant is polymerizable to form a polymerof the discrete polymer layer.
 12. A method as claimed in claim 1,further comprising the steps of: depositing a plurality of discretedroplets of a second liquid on the carrier surface, the second liquidcomprising a mixture of a second electro-optical material and a secondpolymer precursor and forming a further plurality of electro-opticalelements by exposing the plurality of discrete droplets of the secondliquid to a second stimulus for polymerizing the second polymerprecursor into a further discrete polymer layer enclosing the secondelectro-optical material between said further polymer layer and thecarrier surface.
 13. A method as claimed in claim 12, wherein the stepof depositing a plurality of discrete droplets of a first liquid on thecarrier surface and the step of depositing a plurality of discretedroplets of a second liquid on the carrier surface are executedsubstantially in parallel.
 14. A method as claimed in claim 1, whereinthe second electro-optical material comprises a further liquid crystalmaterial.
 15. A method as claimed in claim 12, wherein the second liquidcomprises a second colorant which, during formation of the plurality ofelectro-optical elements, selectively accumulates in the further polymerlayer and has a color which is different from that of the firstcolorant.
 16. A method as claimed in claim 15, wherein the secondcolorant is functionalized with reactive groups adapted to react withthe second polymer precursor during formation of the plurality ofelectro-optical elements.
 17. A method as claimed in claim 16, whereinthe second colorant is polymerizable to form a polymer of the furtherpolymer layer.
 18. A method as claimed in claim 1, further comprisingthe step of depositing a further electrode structure on a polymer layerof the plurality of electro-optical elements.
 19. A method as claimed inclaim 1, further comprising the step of covering the plurality ofelectro-optical elements with a light reflecting coating.
 20. A methodas claimed in claim 1, the method further comprising the step of addinga light-polarizing layer to the carrier the light-polarizing layer beingarranged substantially parallel to the carrier surface.
 21. A method asclaimed in claim 1, further comprising the step of covering theplurality of electro-optical elements with a planarization layer.
 22. Amethod as claimed in claim 1, further comprising the step of providing afurther surface of the carrier with an adhesive layer.
 23. A method ofproducing an electronic device comprising a display area on a part of asurface of a carrier carrying an electrode structure the methodcomprising the steps of: dripping a first liquid on the part of thecarrier surface, the first liquid comprising a mixture of a firstelectro-optical material and a first polymer precursor and forming thedisplay area by exposing the first liquid to a stimulus for polymerizingthe polymer precursor into a discrete polymer layer enclosing the firstelectro-optical material between said polymer layer and the carriersurface.
 24. A method as claimed in claim 23, further comprising thestep of bordering the part of the carrier surface with a dewettingmaterial prior to the dripping of the first liquid on the part of thecarrier surface.
 25. A method as claimed in claim 23, further comprisingthe step of providing a further surface of the carrier with an adhesivelayer.
 26. A method as claimed in claim 25, further comprising the stepof integrating a power supply into the carrier.
 27. A method as claimedin claim 25, further comprising the step of providing the furthersurface with a conductive contact, the conductive contact beingconductively coupled to the electrode structure.
 28. An electronicdevice comprising: a carrier having a surface; and a plurality ofelectro-optical elements positioned on the carrier surface, each of theelectro-optical elements comprising a discrete polymer layer enclosing afirst electro-optical material between said polymer layer and thecarrier surface.
 29. An electronic device as claimed in claim 28,wherein the carrier surface comprises an electrode structure.
 30. Anelectronic device as claimed in claim 28, wherein the carrier surfacecomprises an orientation layer.
 31. An electronic device as claimed inclaim 28, wherein the electronic device further comprises a pattern ofwall structures for creating a plurality of bordered domains on thecarrier surface; an electro-optical element from at least a part of theplurality of electro-optical elements occupying such a bordered domain.32. An electronic device as claimed in claim 28, wherein the pluralityof electro-optical elements are separated from each other by means ofnonwetting regions on the carrier surface.
 33. An electronic device asclaimed in claim 32 wherein the substrate carrier surface is providedwith a plurality of first regions functionalized for selectiveaccumulation of polymer material and a plurality of second regionsfunctionalized for selective accumulation of the electro-opticalmaterial respective first regions being provided between respectivesecond regions and respective regions of a non-wetting material.
 34. Anelectronic device as claimed in claim 29, wherein the firstelectro-optical material comprises a liquid crystal material.
 35. Anelectronic device as claimed in claim 29, wherein the discrete polymerlayer comprises a first colorant.
 36. An electronic device as claimed inclaim 35 wherein the first colorant is chemically bonded to a polymer ofthe discrete polymer layer.
 37. An electronic device as claimed in claim36 wherein the first colorant is polymerized to form a polymer of thediscrete polymer layer.
 38. An electronic device as claimed in claim 32,the electronic device further comprising a plurality of furtherelectro-optical elements positioned over further respective parts of theelectrode structure each of the further electro-optical elementscomprising a further discrete polymer layer enclosing a secondelectro-optical material between said second layer and the carriersurface.
 39. An electronic device as claimed in claim 32, wherein thesecond electro-optical material comprises a further liquid crystalmaterial.
 40. An electronic device as claimed in claim 38, wherein thefurther discrete polymer layer comprises a second colorant having acolor different from that of the first colorant.
 41. An electronicdevice as claimed in claim 40 wherein the second colorant is chemicallybonded to a polymer of the further discrete polymer layer.
 42. Anelectronic device as claimed in claim 41 wherein the second colorant ispolymerized to form a polymer of the further discrete polymer layer. 43.An electronic device as claimed in claim 35, wherein the plurality ofelectro-optical elements carry a further electrode structure.
 44. Anelectronic device as claimed in claim 35, wherein the plurality ofelectro-optical elements are covered by a light reflecting coating. 45.An electronic device as claimed in claim 35, wherein the carriercomprises a light-polarizing layer.
 46. An electronic device as claimedin claim 35, wherein the plurality of electro-optical elements iscovered by a planarization layer.
 47. An electronic device as claimed inclaim 35, wherein the carrier is flexible.
 48. An electronic device asclaimed in claim 35, wherein the plurality of electro-optical elementsare covering a predefined part of the carrier surface.
 49. An electronicdevice as claimed in claim 35, wherein the electronic device is adisplay device.
 50. An electronic device as claimed in claim 35, whereina further surface of the carrier carries an adhesive layer.
 51. Anapparatus for producing an electronic device comprising a plurality ofelectro-optical elements on a surface of a carrier the apparatuscomprising: receiving means for receiving the carrier and depositingmeans for depositing a plurality of discrete droplets of a liquid on thecarrier surface the liquid comprising a mixture of an electro-opticalmaterial and a polymer precursor the depositing means being arrangedopposite the receiving means with at least one of the receiving meansand the depositing means comprising mechanical translation means forchanging an orientation of the depositing means from over a first partof the carrier surface to an orientation over a second part of thecarrier surface.
 52. An apparatus as claimed in claim 51, the apparatusfurther comprising means for forming the plurality of electro-opticalelements by exposing the plurality of discrete droplets to a stimulusfor polymerizing the polymer precursor of a discrete droplet of theliquid into a discrete polymer layer enclosing the electro-opticalmaterial of the discrete droplet between said polymer layer and thecarrier surface.
 53. An apparatus as claimed in claim 51, wherein thedepositing means comprise a printing head having a plurality of nozzles.54. An apparatus as claimed in claim 53, wherein a first subset of theplurality of nozzles is coupled to a reservoir for containing a firstliquid comprising a mixture of a first electro-optical material and afirst polymer precursor and a second subset of the plurality of nozzlesis coupled to a reservoir for containing a second liquid comprising amixture of a second electro-optical material and a second polymerprecursor.